Fire detector devices may be designed to actuate an alarm by closing or opening a circuit on the happening of either one, or both, of two events--when the rate of rise of the temperature of the ambient atmosphere exceeds a predetermined prescribed standard, for example, the 15.degree. F. per minute standard set by Underwriter Laboratories of Canada and Underwriter Laboratories Inc. of the United States, and/or when the ambient temperature exceeds a predetermined fixed temperature.
These detectors must also operate in all environmental conditions, for example, extremes of humidity, variations of heat and cold, and acidic or alkaline vapour mediums.
The necessity for such operation has been recognized by various governmental and independent examining bodies, and standards have been set which the devices must meet or exceed. One such body in the Fire Insurers' Research and Testing Organization (FIRTO for short) of the United Kingdom, who as part of its testing program, has prescribed that such fire detectors must pass a sulphuric acid environment test. This test requires that the fire detector sit in a sulphuric acid environment for a predetermined time and thereafter, still be operable. However, no fire detector that was vented to atmosphere tested with the rate of rise feature before my detector disclosed in Canadian Patent Application Ser. No. 336,801 has remained operable after the time period spent in the sulphuric acid vapour medium. The reason lies in the construction of the vented detector incorporating the rate of rise feature. The chambers between the shell and the diaphragm, and diaphragm and base, must be vented to atmosphere to permit normal atmospheric expansion and contraction due to temperature fluctuations without actuating the alarm. However, if any of the vent apertures are left unprotected in the acidic environment (especially the vent aperture opening from the space between the diaphragm and base) the acidic environment is drawn into the chambers when the detector is "breathing" during normal temperature fluctuations, thus corroding the electrical contacts in the spaces.
In Canadian Patent Application Ser. No. 336,801 I have disclosed an improved fire detector vented to atmosphere, capable of closing or opening an alarm circuit when the rate of rise of the temperature of the ambient atmosphere exceeds a predetermined prescribed rate of rise of temperature comprising a base supporting a diaphragm enclosing a space between the base and diaphragm, a shell secured to the base enclosing a space between the diaphragm and shell, electrical circuit contacts mounted on the base for being closed or opened when the actual rate of rise of the temperature of the atmosphere in the space between the diaphragm and shell exceeds a predetermined rate of rise of temperature, vent apertures through the base from the spaces between the diaphragm and shell, and the diaphragm and base, to the back of the detector, the improvement comprising the vent apertures each being surrounded by an endless wall covered by a closure cap having a top and depending skirt, small projections disposed between the top of the closure cap and the top of the endless wall and thin posts or lugs between the endless wall and depending skirt for spacing the top of the wall from the top of the closure cap and spacing the endless wall from the depending skirt to cover the vent aperture permitting the spaces between the diaphragm and base, and shell and base, to be vented to the atmosphere under normal expansion and contraction of the ambient atmosphere in the fire detector without drawing substantial amounts of air from outside the cover and wall through the vent apertures.
While this proposal went a long way to overcome the problems hereinbefore referred to, nevertheless, small amounts of dust material have from time to time entered the vent aperture.
Detectors of the type described usually carry a heat collecting fin outside the shell and are connected to the shell by a ferrule. The ferrule also carries a fusible link to a detent member within the shell. When heat reaches the fin the heat is transferred from the fin through the ferrule to the fusible link. It is therefore preferable, to provide the heat collecting fin with as large a surface area as possible to maximum heat collection. Where the fin and ferrule were combined in one piece, the fin could not be manufactured of sufficiently large enough diameter at reasonable cost. Where attempts have been made to make the fin-ferrule combination from two components, as was done prior to my invention disclosed in my co-pending Application Ser. No. 336,801 with the fin of large diameter, the union has not yielded a satisfactory result.
In my co-pending Application Ser. No. 336,801 I disclosed an improved fire detector having alarm actuating means for actuating an alarm at a predetermined temperature and a fin for collecting heat from the ambient atmosphere, the fin being connected by a ferrule to the alarm actuating means for actuating the alarm at the predetermined temperature, the connection between the fin and the ferrule having been formed by causing metal in an end portion of the ferrule to flow over fin metal surrounding the aperture of the fin through which aperture the ferrule extends to provide a thin layer of ferrule metal over fin metal.
As a result, the metal of the ferrule was married to the metal of the fin. In that way, an anodized aluminum fin of relatively large diameter (and thus non-solderable, but immune to sulphuric acid) could be intimately connected to solderable blind hole tin plated aluminum ferrule.
However, it has been found that in some instances during the marrying of the fin to the ferrule, the pressure to hold the fin to the ferrule while ferrule material was caused to flow radially over the fin material, distorted the fin and in some of those instances, the pressure applied in one area caused the connection of the fin to the ferrule to buckle and loosen in another area.
It is therefore an object of this invention to provide an improved fire detector and structural components useful therefor.
Further and other objects of the invention will be realized by those skilled in the art from the following summary of the invention and detailed description of embodiments thereof.